全文获取类型
收费全文 | 7419篇 |
免费 | 239篇 |
国内免费 | 332篇 |
专业分类
化学 | 611篇 |
晶体学 | 42篇 |
力学 | 1036篇 |
综合类 | 9篇 |
数学 | 4010篇 |
物理学 | 2282篇 |
出版年
2024年 | 7篇 |
2023年 | 69篇 |
2022年 | 63篇 |
2021年 | 73篇 |
2020年 | 125篇 |
2019年 | 119篇 |
2018年 | 120篇 |
2017年 | 142篇 |
2016年 | 159篇 |
2015年 | 167篇 |
2014年 | 403篇 |
2013年 | 591篇 |
2012年 | 333篇 |
2011年 | 522篇 |
2010年 | 432篇 |
2009年 | 483篇 |
2008年 | 564篇 |
2007年 | 566篇 |
2006年 | 352篇 |
2005年 | 280篇 |
2004年 | 268篇 |
2003年 | 250篇 |
2002年 | 199篇 |
2001年 | 167篇 |
2000年 | 191篇 |
1999年 | 164篇 |
1998年 | 146篇 |
1997年 | 147篇 |
1996年 | 115篇 |
1995年 | 114篇 |
1994年 | 89篇 |
1993年 | 56篇 |
1992年 | 56篇 |
1991年 | 30篇 |
1990年 | 41篇 |
1989年 | 26篇 |
1988年 | 19篇 |
1987年 | 22篇 |
1986年 | 32篇 |
1985年 | 35篇 |
1984年 | 33篇 |
1983年 | 27篇 |
1982年 | 27篇 |
1981年 | 27篇 |
1980年 | 37篇 |
1979年 | 35篇 |
1978年 | 23篇 |
1977年 | 25篇 |
1976年 | 8篇 |
1974年 | 3篇 |
排序方式: 共有7990条查询结果,搜索用时 656 毫秒
41.
Noureddine Igbida 《Journal of Mathematical Analysis and Applications》2007,335(2):1061-1078
In this paper, we study the nonlinear evolution equation of Hele-Shaw type with dynamical boundary conditions. That is, the equation ut=Δw+f where u∈H(w) and H is the Heaviside function, with boundary condition μ(x,w)t∂w+k∇w⋅ν=g, where ν denotes the outward normal vector of the fixed boundary of the domain. We prove existence, uniqueness and some qualitative properties of the solution. 相似文献
42.
In this paper we consider a class of nonlinear delay partial difference equations and a class of linear delay partial difference equations with variable coefficients, which may change sign. We obtain oscillation criteria for these equations. There are no results for the oscillation of these equations up to now. 相似文献
43.
Jonathan M. Borwein 《Optimization Letters》2007,1(1):21-32
This paper is a companion to a lecture given at the Prague Spring School in Analysis in April 2006. It highlights four distinct variational methods of proving that a finite dimensional Chebyshev set is convex and hopes to inspire renewed work on the open question of whether every Chebyshev set in Hilbert space is convex. 相似文献
44.
45.
Discrete global descent method for discrete global optimization and nonlinear integer programming 总被引:2,自引:0,他引:2
A novel method, entitled the discrete global descent method, is developed in this paper to solve discrete global optimization
problems and nonlinear integer programming problems. This method moves from one discrete minimizer of the objective function
f to another better one at each iteration with the help of an auxiliary function, entitled the discrete global descent function.
The discrete global descent function guarantees that its discrete minimizers coincide with the better discrete minimizers
of f under some standard assumptions. This property also ensures that a better discrete minimizer of f can be found by some classical local search methods. Numerical experiments on several test problems with up to 100 integer
variables and up to 1.38 × 10104 feasible points have demonstrated the applicability and efficiency of the proposed method. 相似文献
46.
T. I. Khabakhpasheva 《Fluid Dynamics》2003,38(4):592-600
The problem of surface wave diffraction on a floating elastic plate is considered. The relation between the parameters of the elastic vibrations of the plate and the transmitted and reflected wave amplitudes is investigated. It is shown that the maximum amplitudes of the plate stresses and deflections depend nonmonotonically on the incident wave frequency and are reached simultaneously with the maxima of both the transmission coefficient and the length of the wave penetrating into the plate. This makes it possible to use the transmission coefficient as a parameter for investigating the maximum and minimum amplitudes of the hydroelastic vibrations of the plate. As an example, this criterion is used to minimize the vibrations of a plate whose leading edge is elastically connected to the bottom. 相似文献
47.
锂锰尖晶石红外光谱的研究 总被引:10,自引:1,他引:9
本文对锂锰尖晶石的红外光谱进行了研究。由于锂锰尖晶石的晶体结构属于Fd3m空间群,锂离子占据四面体空隙(8a位置),锰离子占据八面体空隙(16d位置)。根据群论的知识,对锂锰尖晶石晶体中离子的振动方式与红外活性之间的内在关系进行了讨论。并列出了锂锰尖晶石的红外光谱实验数据。通过理论分析,我们推断:位于618.6和501.5cm~(-1)的红外吸收带分别来源于Mn(Ⅳ)-O和Mn(Ⅲ)-O键在晶体中的不对称伸缩振动(单元为Mn(Ⅳ)O_6和Mn(Ⅲ)O_6八面体),位于1124cm~(-1)的弱红外吸收带来源于Li-O键的不对称伸缩(单元为LiO_4四面体)。还有一些低于400cm~(-1)的可能吸收带在400~4000cm~(-1)范围内未能检测到。这一结论的可靠性通过锂锰尖晶石和掺杂的锂锰尖晶石的红外光谱实验数据得到证实。 相似文献
48.
This paper discusses a class of second-order derivative nonlinear Schrödinger equations which are used to describe the upper-hybrid oscillation propagation. By establishing a variational problem, applying the potential well argument and the concavity method, we prove that there exists a sharp condition for global existence and blow-up of the solutions to the nonlinear Schrödinger equation. In addition, we also answer the question: how small are the initial data, the global solutions exist? 相似文献
49.
A. Aghajani 《Journal of Mathematical Analysis and Applications》2007,326(2):1076-1089
We consider the nonlinear Euler differential equation t2x″+g(x)=0. Here g(x) satisfies xg(x)>0 for x≠0, but is not assumed to be sublinear or superlinear. We present implicit necessary and sufficient condition for all nontrivial solutions of this system to be oscillatory or nonoscillatory. Also we prove that solutions of this system are all oscillatory or all nonoscillatory and cannot be both. We derive explicit conditions and improve the results presented in the previous literature. We extend our results to the extended equation t2x″+a(t)g(x)=0. 相似文献
50.